1. Field of the Invention
This invention relates to treatment chemicals for recirculating water of a spray booth which enable the reuse of treated water by separating paint scum from scrubbing water contaminated with excess paint dusts in the painting system of automobiles, household electric appliances, etc.
2. Description of Prior Art
To separate excess paint scum from scrubbing water, various inorganic coagulants with or without an organic high molecular weight polymer have been used to coagulate and flocculate them to larger flocs which easily settle or float, and the thus treated water is reused as the recirculating water of the paint booth. Acidic coagulants such as alum, aluminum chloride, polyaluminum chloride, ferric chloride, zinc chloride, zinc sulfate, etc. have been used as inorganic coagulants; however, the pH of booth water thus becomes acidic necessitating the use of caustic soda to adjust the pH in the optimum range for floc formations. The thus formed chloride ion or sulfate ion remains and concentrates in the recirculating water when the system is closed tightly and the water mist entrained into and adhered to the booth air duct may cause severe corrosion, which sometimes breaks air ducts and causes the plant to be closed.
The separated scum also contains chloride or sulfate which release hydrogen chloride or sulfur dioxide in the incinerator resulting not only in severe air pollution but also in short life of the incinerator. A large investment is necessary in order to install equipment for preventing air pollution caused by such harmful gases.